Ribosome Inactivating Protein Research

1. Biota orientalis ribonuclease specifically cleaves a single phosphodiester bond in rat 28S ribosomal RNA and inactivates ribosome: A unique ribonuclease named Biota orientalis ribonuclease (Biota orientalis RNase) is purified to homogeneity from mature seeds of oriental arborvitae (Biota orientalis). The molecular mass of Biota orientalis RNase is about 13 kDa. When the concentration of Mg2+ is 25 mM in the incubation buffer, the ribonuclease specifically hydrolyzes the phosphodiester bond between C4453 and A4454 in region K (a region in domain VII) of 28S RNA in rat ribosome, resulting in inactivation of ribosome. The region around C4453-A4454 in rat 28S rRNA is named "Biota orientalis RNase region". Rat ribosome treated by Biota orientalis RNase produces a small RNA fragment (S-fragment) that contains 333 nucleotides from the 3'-terminus of rat 28S rRNA. The distance between the cleavage-sites of α-sarcin (G4325) and Biota orientalis RNase (C4453) is 128 nucleotides. Under restricted conditions (25 mM Mg2+), the substrate specificity of Biota orientalis RNase is extremely high: it acts only on the "Biota orientalis RNase region" of the largest RNA in ribosomes from certain eukaryotes. The ribosome specifically damaged by Biota orientalis RNase is unable to IV中国科学院生物化学和细胞生物学研究所 博士学位论文 摘要 EF-1α-dependently bind aminoacyl-tRNA, whereas the formation of the EF-2/GDP/ribosome complex is not affected. It is proposed that Biota orientalis RNase inactivates ribosome at least partially by interfering with the EF-1α-dependent binding of aminoacyl-tRNA to ribosome. Biota orientalis RNase might be a useful tool in studying the structure/function of ribosome. Compared with α-sarcin that is a kind of ribosome-inactivating protein (RIP), Biota orientalis RNase is actually a RIP.